Barrel life's based on how accurate the rifle barrel is when it's new.

If it starts out at no worse than 1/4 MOA, it'll last about 3000 rounds burning 1 grain of powder for each square millimeter of the bore's cross sectional area. Example, .308 Win. with 45 grains of powder, 45 square millimeters of bore cross sectional area. Or the 22 PPC; 22 grains of powder. The 6mm PPC; 28 grains of powder. These quarter-inchers all last about 3000 rounds for tack-driving accuracy. Best test of barrel life for the .308 Win. is that Sierra Bullets replaces their accuracy test barrels about every 3000 rounds. That's when they stop shooting 1/4 MOA at 200 yards with their best match bullets and test groups have started up into the 3/8 MOA range.

Barrels starting out at 1/2 to 3/4 MOA will get about twice as much barrel life. And barresl starting out at 1 to 1-/4 MOA may get four times as much. Typical are 30 caliber service rifles that last about 9,000 to 10,000 rounds for the accuracy their specs state.

Double the powder charge for a given bore diameter and barrel life drops by 75%. Huge 30 caliber magnums burning 90 grains of powder get 700 to 800 rounds of barrel life if they start out at 1/4 MOA.